In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
For example, wireless devices incorporating radio access technologies (RATs) defined by the telecommunications standards Global System for Mobile Communications (GSM), Wideband Code Division Multiple Access (WCDMA), Long Term Evolution (LTE), etc., may be configured to perform specific services, such as emergency calls. Such specific services may further involve the wireless device to use positioning technologies such as the Global Positioning System (GPS), or the Globalnaya navigatsionnaya sputnikovaya Sistema (GLONASS), also known as the Global Navigation Satellite System.
In the United States, the Federal Communications Commission (FCC) is forcing network operators to implement solutions to accurately locate wireless devices performing emergency calls within their networks. At the present date, these accuracy requirements are: 1) 50 meters for 67% of the calls, and 150 meters for 95% of the calls when the position is determined by the wireless device (so-called wireless device-based determination), and 2) 100 meters for 67% of the calls, and 300 meters for 95% of the calls when the position is determined by the network as assisted by the wireless device (so-called wireless device-assisted determination).
For GSM/WCDMA-type networks, network operators have adopted a mechanism called Network Induced Location Request (NILR), see 3GPP TS 23.271—“Functional stage 2 description of Local services (LCS)”. In general terms, when the wireless device triggers an emergency circuit switched (CS) call, the GSM/WCDMA-type networks start a NILR positioning procedure in parallel with the emergency call setup. The output of this procedure is the location information of the wireless device. The positioning method used is decided by the radio access network (RAN).
In order to achieve, and possibly exceed the FCC accuracy requirements, global navigation satellite system (GNSS) positioning technologies such as GPS (and more recently also GLONASS) are used, provided that the wireless device supports them. For both wireless device-based and wireless device-assisted approaches, the wireless device may be regarded as taking a vital role in determining its location either by calculating it itself (wireless device-based) or by providing the RAN with the GNSS measurement results needed for the calculation (wireless device-assisted).
In scenarios where a wireless device is operatively connected to an LTE-type network and not capable to perform Internet Protocol Multimedia Subsystem (IMS) emergency calls, an emergency call attempt will results in a CS fallback procedure as described in 3GPP TS 23.272—“Circuit Switched (CS) fallback in Evolved Packet System (EPS)”. Examples of some conditions are (but not limited to) the following: 1) the wireless device does not have Voice over LTE (VoLTE) capabilities, 2) the wireless device has VoLTE capabilities but is registered over a network which does not support VoLTE, and 3) the wireless device has VoLTE capabilities but is registered over a network which does not support an IMS emergency services (this information is in LTE broadcasted in the Broadcast Control Channel (BCCH) downlink (DL) Synchronization Channel (SCH) first system information block (SIB1)).
In general terms, the CS fallback procedure requires the wireless device to perform a RAT change; from LTE to WCDMA, or from LTE to GSM, for example according to network deployment and reported capabilities of the wireless device. The LTE RAN triggers the RAT change by sending to the wireless device a Radio Resource Control (RRC) Connection Release message, which includes information elements for redirection of the wireless device to the new RAT.
Once the wireless device synchronizes with the network node in the new RAT, the emergency call will be set up and the NILR positioning procedure will then take place.
In scenarios where a wireless device is operatively connected to an LTE network and attempting to set up an emergency call via a CS fallback procedure, existing mechanisms thus require the wireless device to perform a RAT change before receiving the NILR request with GNSS assistance information. This delays the location determination of the wireless device, which location determination procedure is triggered only once the wireless device is redirected to the new RAT.
In scenarios where the wireless device is capable to perform IMS emergency calls, a positioning procedure may be started already when the wireless device is operatively connected to an LTE network. However, in the occurrence of Single Radio-Voice Call Continuity (SRVCC) the positioning procedure would be aborted. Thus, in scenarios where the wireless device is performing an IMS emergency call, a positioning procedure started when the wireless device is operatively connected to the LTE network will be aborted if an SRVCC procedure is triggered.
Hence, there is still a need for an improved position determination of a wireless device.